The invention relates to a method and apparatus for producing extra-wide veneers and from them the production of endless laminated wood boards by gluing and pressing a chain of veneers combined from these extra-wide veneers one over the other and behind one another in a plurality of layers.
In the production of laminated wood veneer boards by the method of DE 196 27 024 A1, veneers with a width of 1200 to 1400 millimeters are used exclusively today. The veneers are obtained by the peeling process from logs and then dried. The veneers shrink in the drying by about 0.2-0.3% in the direction of the grain and by 5-8% across the grain. Since the veneers do not shrink evenly, the width of a veneer accurately cut before drying varies after drying by about xc2x125 mm. After drying the veneers are sorted into various qualities and the appropriate classes of veneer are delivered to the production line for the production of laminated wood boards.
There they are stacked together to form a growing pack, and a previously defined outer edge of the pack serves as the alignment edge. The assembled veneer pack has on the alignment edge only a minimum misalignment between the individual veneers, which is due to the accuracy with which they were aligned and stacked. As a rule it amounts to xc2x110 mm and results in a maximum misalignment of 20 mm. On the opposite side the result is a misalignment of the veneer edges of typically 70 mm, composed of the sum of the alignment and stacking tolerances plus the tolerances in the veneer width.
After the pressing operation the finished veneer piece is trimmed on both sides so as to obtain clean edges. The trimming width is determined by the maximum offset of the veneers on the particular side.
Assuming a Gaussian normal distribution of the tolerances in the widths, the alignment and the stacking, the result is then a material loss of 50% of the trimming width, and consequently of 45 mm of the production width.
On the basis of a small production width of 1200 to 1400 mm, the result is a loss of material of 3.2 to 3.75%. In the manufacture of laminated veneer products the wood costs amount to 65 to 75% of the production costs. A reduction of the material losses is consequently very interesting from the economic point of view.
An increase in the production width first appears to be the most promising way. It is true that the width tolerances increase linearly with the width of the veneers, so that only uniform alignment and stacking tolerances will lead to a lower percentage of material loss. If, however, the overall process is considered, the greater the veneer width is, the less will be the yield from the log-peeling process, since it is harder to find continuous veneers of great width with no defects. Furthermore, it would be problematic in the peeling process to change the standard width, since a considerable percentage of the veneers produced will be found unsuitable for laminated wood boards when sorted afterward, due to insufficient strength and will find use as plywood veneer. It is furthermore advantageous if veneers can be purchased on the free market if needed. In the conventional production of veneers and veneer plywood, in which veneers of a standard width of 1330 mm are used and a trimmed board of 1220 mm can be produced with the stacking and alignment tolerances, 15 flanges can be made with a width of 75 mm with a saw kerf of 3 mm. A scrap with a width of 50 mm is wasted and goes into the shredder. That is another 4% loss of material.
The invention is addressed to the task of providing a method whereby laminated wood boards with extra-widths up to about 3600 mm can be made, these boards being suitable for the production of laminated veneer boards of optimum quality, and of creating an apparatus for the practice of the method.
As for the method, the accomplishment of this task consists in the fact that the veneers arriving one after the other with a producible width b and with the grain running transversely are combined to make a chain of veneers, sewn together or joined with adhesive tape at the meeting edges, and veneers with a given extra-width (B) are severed with the grain such that the seams or junctions in the chain of veneers are distributed irregularly across the width of the laminated wood board, not aligned one over the other.
The solution for an apparatus of the first embodiment consists in the fact that, in a continuously operating manner, veneers with their grain and their producible width oriented across the feed direction are lifted by the vacuum conveyor belt for transfer to a double belt conveyor system; following the double belt conveyor system the apparatus has a sewing machine for sewing together the abutments between two oncoming veneers, and the chain of veneers thus formed can be passed onto a second double conveyor belt system, the chain of veneers is severable by means of a cutting apparatus to a given length equal to the corresponding width of an extra-wide laminated veneer board, and that the extra-wide laminated veneer boards thus severed can be laid onto a feed belt running at right angles thereto, with their grain now running in the direction of the feed to the LVL production line.
The solution for an apparatus of a second embodiment consists in the fact that, in a continuously operating manner, veneers with their grain and their producible width running transversely across the feed direction are lifted from the vacuum conveyor belt for transfer to a double belt conveyor, the apparatus following the double belt conveyor has a sewing machine for sewing together the abutting edges of two veneers, and the chain of veneers thus formed can be transferred to a second double belt conveyor, the chain of veneers can be cut by a cutting apparatus to a given length equal to the corresponding width of an extra-wide laminated wood board, so that the extra-wide veneer pieces thus severed can be laid onto a pallet to form a supply stack.
With the method and apparatus according to the invention, the possibility is for the first time offered of adapting the production width in laminated wood manufacture to the width of the end product, i.e., to a multiple thereof, so as to avoid scraps left over after the finished board is divided up. Due to the starting veneer""s width tolerance of xc2x125 mm and to the virtually perfect cut width of the laminated veneer boards, the junction d shifts irregularly within the extra-wide laminated veneer boards. The junction points d are thus distributed across the entire board and no longer constitute a weak point. Even the great gap that can form due to lack of trimming has no weakening effect on the finished product, since at no point are several junction points situated one over the other. Like the knot-holes present in great numbers in the commonly used softwoods, the offset seams above and below in the laminated wood board compensate for one another; in other words, the composed veneer layers placed on top or below compensate for the weak point. Thus all sections of the laminated wood board can be used without exception for load-bearing components.
For the cover layers, i.e., top and bottom veneer of the laminated wood boards, the starting veneers can be trimmed before joining. Thus a rectilinear edge and a gap-free abutment between veneers can be obtained. For aesthetic reasons this is necessary for some applications. The loading stations must be provided with an additional knife for this purpose and a scanner to detect irregularity in the veneer edge. For special applications, however, all loading stations can be provided with the additional knife in order to obtain gap-free seams in all layers of the boards.
Additional advantageous measures and embodiments of the subject of the invention will be found in the subordinate claims and in the following description and drawing.